1. Technical Field
The present invention relates to a technology for driving electro-optical materials, such as liquid crystals.
2. Related Art
In an electro-optical apparatus, such as a liquid crystal device, many pixels are disposed in a matrix, and each row of pixels is selected by multiplex driving so that an image signal is supplied to each of the selected pixels. In this configuration of the electro-optical apparatus, if, in particular, the total number of pixels is increased to achieve higher precision, the duty ratio (reciprocal of the total number of scanning lines) is decreased, and the time for supplying an image signal to each pixel cannot be sufficiently ensured. To solve this problem, a so-called “multiple matrix technology” has been proposed in, for example, JP-A-2002-90765 (FIG. 10).
An electro-optical apparatus (liquid crystal device) using this multiple matrix technology includes a first substrate and a second substrate between which a liquid crystal is sealed. As shown in FIG. 9, a plurality of scanning lines 91 extending in the X direction are formed on the surface of the first substrate, a plurality of first data lines 921 and a plurality of second data lines 922 extending in the Y direction are formed on the surface of the second substrate. Many pixel electrodes 93 are disposed on the second substrate in a matrix. The pixel electrodes 93 in the odd-numbered rows are connected to the adjacent first data lines 921, and the pixel electrodes 93 in the even-numbered rows are connected to the adjacent second data lines 922. As shown in FIG. 9, two pixel electrodes 93 adjacent to each other in the Y direction oppose the same scanning line 91. Accordingly, two rows of pixels are formed for each scanning line 91. With this configuration, the duty ratio can be increased by about twice (assuming the same number of pixels) compared to that in an electro-optical apparatus in which only one pixel is formed at each intersection between a scanning line and a data line.
It is known that the application of DC components of a voltage deteriorate optical characteristics of electro-optical materials, in particular, liquid crystals. AC driving is required to suppress such deterioration in the optical characteristics. In AC driving, a positive voltage and a negative voltage relative to a predetermined voltage are alternately applied to pixels for the alternating rows. However, if this AC driving is applied to a multiple-matrix electro-optical apparatus, display irregularities occur in the shape of strips in the X direction in units of two rows of pixels corresponding to one scanning line 91. This problem is discussed in detail below.
When AC driving is applied to a multiple-matrix electro-optical apparatus, the polarity of the voltage applied to two rows of pixels corresponding to one scanning line 91 becomes opposite to that applied to two rows of pixels corresponding to the adjacent scanning line 91. That is, if, as shown in FIG. 9, a positive (+) voltage is applied to two rows of pixels corresponding to the k-th (k is a natural number) scanning line 91, a negative (−) voltage is applied to two rows of pixels corresponding to the (k+1)-th scanning line 91. The relationship of the positive and negative polarities is changed in, for example, every vertical scanning period.
Let us focus on each pixel of the i-th (i is a natural number) row to which a positive voltage is applied. Each pixel of the i-th row is adjacent to a corresponding pixel of the (i+1)-th row on the positive Y direction side and to a corresponding pixel of the (i−1)-th row at the negative Y direction side. The pixels of the (i+1)-th row are applied with a negative voltage and the pixels of the (i−1)-th row are applied with a positive voltage. Since the same polarity of the voltage (positive voltage) is applied to the pixels in the i-th row and the pixels in the (i−1)-th row, horizontal (i.e., in-plane direction in which pixels are disposed) electric fields are not generated between the pixels of the two rows. In contrast, since different polarities of voltages are applied to the pixels in the i-th row and the pixels in the (i+1)-th row, horizontal electric fields are generated between the pixels of the two rows (in particular, at interfaces between the two rows). Accordingly, liquid crystals of the pixels in the i-th row adjacent to the corresponding pixels in the (i+1)-th row are aligned in a direction different from a desired direction. As a result, the grayscale of a portion C1 shown in FIG. 9 becomes different from that of a portion C2 shown in FIG. 9 adjacent to the pixels in the (i−1)-th row. This difference in the grayscale is observed as display irregularities by users.
In an electro-optical apparatus in which only one pixel is disposed at each intersection between a scanning line and a data line, horizontal electric fields are also generated in adjacent pixels in the Y direction. In this configuration, however, display irregularities equally occur to all the pixels, and thus, this does not present any problem in the visual sense. In contrast, in a multiplex-matrix electro-optical apparatus, although horizontal electric fields are generated in a portion adjacent to the pixels in one adjacent row (i.e., pixels to which a voltage having the opposite polarity is applied), horizontal electric fields are not generated in a portion adjacent to the pixels in the other adjacent row (i.e., pixels to which a voltage having the same polarity is applied). Because of this non-uniformity, display irregularities occur.